Of late, it has become a subject of discussion that more hydrocarbon is included in exhaust gas from a two cycle internal combustion engine and therefore the exhaust gas from the two cycle engine tends to be strongly regulated.
Accordingly, there has been desired a development of such arts as reduce an amount of hydrocarbon in the exhaust gas without damaging a feature of the two cycle internal combustion engine which can provide a high output therefrom in spite of its lightness and small size.
A fuel direct injection art in which fuel (generally gasoline) is directly injected into fuel chambers of respective cylinders is remarkably noted as one of them.
A main one of reasons for which the amount of hydrocarbon in the exhaust gas from the two cycle internal combustion engine is more than that from the four cycle internal combustion engine is that a part of mixed gas which is produced by being previously compressed in a crank case is blown out through exhaust ports when it sweeps combusted gas in the cylinders. This has been called "Blown Out Action".
It has been considered that the fuel is supplied to the cylinders by means of cylinder fuel direct injection in which the fuel is injected directly into the respective cylinders after all of scavenging ports and exhaust ports provided in cylinder walls are closed in place of the prior art in which the mixed gas produced by a carburetor and fuel injectors injecting the fuel into intake pipes, respectively, is supplied through the crank case to the respective cylinders. This fuel cylinder direct injection makes just air blown out through the exhaust ports when the combusted gas is swept, which enables the amount of hydrocarbon to be reduced in the exhaust gas.
In order to apply the cylinder fuel direct injection to the two cycle internal combustion engine, fuel injection valves (injectors) are required to be provided in cylinders, respectively, so as to inject the fuel directly to combustion chambers of the respective cylinders and the fuel should be supplied from a fuel pump to the respective fuel injection valves under pressure higher than an output pressure of the fuel injection pump. The amount of fuel to be injected into the respective cylinders will be expressed by a function of a difference pressure between a pressure of fuel applied to the fuel injection valves for the respective cylinders and a pressure in the respective cylinders when the fuel is to be injected and time (injection tine) for which the fuel injection valves are opened.
In order to make the cylinder fuel direct injection, the predetermined amount of fuel should be injected for extremely short period after both of the respective scavenging ports and exhaust ports are closed and before an ignition is made. Thus, there should be required higher fuel pressure applied from the fuel pump to the fuel injection valves as the injection time is shorter.
Since the output pressure of the fuel injection valve is extremely higher due to a compression stroke of the engine during the period for which the cylinder fuel direct injection is made (the period for which both of the scavenging ports and the exhaust ports are closed), there should be used a high output pressure rotary pump which provides a higher output pressure therefrom so as to inject the predetermined amount of fuel while overcoming the output pressure of the fuel injection valves.
The prior art two cycle internal combustion engine has a fuel pump not required to have an high output pressure although it has the fuel injection valves because the fuel is injected into the intake pipes or into the crank case. Thus, in the prior art, there has been a diaphragm type fuel pump which is driven by a pressure variation in the crank case or a rotary fuel pump which is driven by a battery driven motor. Both of the fuel pumps are not required to utilize the output of the engine for driving it.
Such a diaphragm type fuel pump as driven by a pressure variation in the crank case can hardly feed the fuel under the higher pressure overcoming the cylinder pressure at the compression stroke thereof. If such a rotary fuel pump as driven by a battery driven motor is utilized to feed the fuel under the higher pressure overcoming the output pressure of the cylinder pressure at the compression stroke thereof, then it is required to be disadvantageously large-sized because of the large-sized motor therefor. With the large-sized motor provided on the engine for driving the fuel pump, the engine is also large-sized. This will loss the advantage of the two cycle engine which can produce a higher output in spite of its small size.
It is considered that the fuel pump will be driven by a crank shaft of the engine while the higher output pressure overcoming the cylinder pressure at the compression stroke is generated. However, one end of the crank shaft of the engine is used for driving a main load while the other end is connected to a flywheel. Therefore, it is hard to drive the fuel pump by the crank shaft while generating such higher output pressure overcoming the cylinder pressure.
It is considered that the fuel pump to be driven while generating such higher output pressure will have a rotary drive shaft connected to a portion of the crank shaft end protruded from the flywheel. With such a crank shaft driven fuel pump used, the engine will be elongated in a longitudinal direction because the crank shaft of the engine will be longer and in addition the fuel pump is disposed in series with the flywheel. This causes the engine to be disadvantageously large-sized.
If the fuel pump is provided on the end of the crank shaft protruded from the flywheel, then a stator will be hardly provided on the side of the flywheel.
If the fuel pump generating such a higher output pressure overcoming the cylinder pressure is driven by the crank shaft, it is required to be resistant to the high revolution of the engine.
A conventional high output pressure fuel pump for a fuel direct injection type four cycle internal combustion engine has been mass produced. Such a mass production type high output pressure fuel pump can be hardly used for being mounted on the crank shaft of the two cycle internal combustion engine. In order to drive the fuel pump from the crank shaft of the two cycle engine, it is required to be designed and produced as a specific pump which can be resistant to the high revolution thereof. This causes the fuel pump to be expensively provided.